A simple micro-photometric method for urinary iodine determination.

Background: Urinary iodide concentration (UIC) is useful to evaluate nutritional iodine status. In clinical settings UIC helps to exclude blocking of the thyroid gland by excessive endogenous iodine, if diagnostic or therapeutic administration of radio-iodine is indicated. Therefore, this study established a simple test for the measurement of UIC. Methods: UIC was analyzed in urine samples of 200 patients. Samples were pre-treated at 958C for 45 min with ammonium persulfate in a thermal cycler, followed by a photometric Sandell-Kolthoff reaction (SK) carried out in microtiter plates. For method comparison, UIC was analyzed in 30 samples by inductivity coupled plasma mass spectrometry (ICP-MS) as a reference method. Results: Incubation conditions were optimized concerning recovery. The photometric test correlated well to the reference method (SKs0.91*ICP-MSq1, rs0.962) and presented with a functional sensitivity of 20 mg/L. UIC of patient samples ranged from -20 to 750 mg/L (median 110 mg/L); 90% of the urine samples had iodide concentrations below 210 mg/L. Conclusion: The modified SK-test takes approximately 90 min for analyses of 20 urine samples compared with 27 h for ICP-MS. The photometric test provides satisfactory results and can be performed with the basic equipment of a clinical laboratory. *Corresponding author: Dr. Gabriele Grimm, Department of Laboratory Medicine, Medical University of Vienna, Austria Phone: q43 1 40400 5342, Fax: q43 1 40400 5761, E-mail: gabriele.grimm@meduniwien.ac.at Received March 15, 2011; accepted May 20, 2011; previously published online June 25, 2011